Revert back to win 7 ultimate from win 8.1 pro

[iWinButton]

I had win 7 ultimate on my computer and then got a free copy {MSDN Subscription} of windows 8.1 Pro. I installed it and have used it for a bit but I have decided I hate it lol. I want my windows 7 ultimate back. I do have the windows.old file still as I never got rid of it. Can I just put my win7 ultimate back on my bootable thumb drive and reinstall then erase the win 8.1 stuff later? Or is there a way just to restore back to the system restore point from before I installed windows 8.1?

 

[ex_bubblehead]

Full wipe and reinstall is the only way to go backward.